Figure
1. Area shaded in red is downstream of Vicksburg
Figure
2. Avg. Annual Precipitation, mm/d
Figure
3. Avg. Annual Runoff, mm/d
This page provides an estimation of undepleted runoff for the Mississippi River basin, for comparison of simulated runoff. The estimation of runoff includes two steps: 1) Estimating unregulated (undepleted) flows at the USGS gauge at Vicksburg, MS; and 2) Extrapolating this value to the entire Mississippi River basin. Based on these calculations, the annual Mississippi River basin runoff for the period 1996-99 is estimated to be 0.630 mm/d. Values for other periods can be estimated from the table of annual runoff values below.
Since none of the models included in the WEBS effort simulate water management effects, the runoff against which they are compared likewise should not reflect these, and the comparison should be done with undepleted flows. Portions of the Mississippi River basin are relatively unaffected by water management, at least for long-term total runoff. However, the effects are more pronounced in other basins (such as the Missouri), as seen below.
Estimated streamflow depletions upstream of Vicksburg, MS for 1995
|
Gauge/Location |
Drainage Area, mi2 |
Depletions, cfs |
|---|---|---|
|
Ohio River nr Metropolis, IL |
203,000 |
219(b) |
|
Upper Mississippi, at Alton, IL |
171,500 |
539(b) |
|
Missouri River at Hermann, MO |
52,400 |
27,642(c) |
|
Arkansas R. at Little Rock, AR |
158,090 |
7,090(d) |
|
White R. at Devalls Bluff, AR |
23,431 |
1,091(d) |
|
Remaining (Lower Mississippi) |
60,279(a) |
3,710(e) |
|
TOTAL - MISSISSIPPI R. AT VICKSBURG, MS |
1,140,500 |
40,291 |
(a) Remaining amount for drainage area is the difference between Vicksburg and the sum of all others.
(b) Source: "Estimated Use of Water in the United States in 1995," Solley, W.B., R.R. Pierce, and H.A. Perlman, U.S.Geological Survey Circular 1200, 1998. Values are for consumptive use due only to irrigation.
(c) Source: "Reservoir Regulation Studies - Daily Routing Model Studies, Missouri River Master Water Control Manual Review and Update Study," U.S. Army Corps of Engineers Northwest Division, 1998. Only the values for 1995 are used, to be consistent with the other source of depletion data.
(d) Same source as (b), but adjusts the depletion amount given for the Arkansas-Red-White system based on the relative contributing area of the gauge compared to the total including the Arkansas River at Little Rock, the White River at Devalls Bluff and the Red River at Shreveport. 65% of the area is attributed to the Arkansas River, 10% to the White River, with the remaining 25% being the Red River, which joins the Mississippi River downstream of Vicksburg, MS.
(e) Same source as (b), but adjusts the amount given for the Lower Mississippi basin based on the relative contributing area of the Lower Mississippi basin (the portion above the Vicksburg), which amounts to 41% of the total Lower Mississippi area.
A seasonal breakdown of depletions can be derived by assuming depletions follow the seasonal evaporation cycle of the basin (based on the VIC model results averaged for 1988-99).
Fraction of annual total evaporation (and depletion) occurring in each season
|
|
DJF |
MAM |
JJA |
SON |
|---|---|---|---|---|
|
Depletion |
0.171 |
0.289 |
0.319 |
0.221 |
Since the distribution of runoff is far from uniform through the Mississippi River basin, with a concentration of much greater values in the southeastern area, the basin-wide average for the region upstream of Vicksburg is substantially lower than that for the entire basin. The area of the basin contributing to flow at Vicksburg, MS is shown below, as is the distribution of precipitation (gridded gauge values) and runoff (from the VIC model, driven by gridded gauge precipitation).
|
|
|
|
|---|
The undepleted runoff can be scaled using a ratio of runoff produced upstream of Vicksburg to that of the entire Mississippi basin, based on VIC model results (note that only the ratios are taken from model simulations, and not the predicted runoff).
The runoff values for the entire Mississippi River basin are derived by multiplying the annual undepleted runoffs for each year by the annual ratios. These undepleted runoff values for the Entire Mississippi River basin are recommended for comparison with results, rather than raw gauge flows at Vicksburg. The raw flows at Vicksburg are affected by water management and are for a drainage area different than that simulated by the models (Figure 1).
Calculation of Runoff Values (mm/d) for Entire Mississippi River basin.
|
Year |
Gauge Flow at Vicksburg, cfs |
Depletions, cfs (a) |
Undepleted Flow at Vicksburg, cfs (b) |
Avg. Annual Runoff at Vicksburg, mm/d |
Ratio of Runoff of Mississippi basin to Upstream of Vicksburg (c) |
Avg. Annual Runoff for Entire Mississippi River basin, mm/d |
|---|---|---|---|---|---|---|
|
1988 |
439,000 |
34,100 |
473,000 |
0.392 |
1.153 |
0.452 |
|
1989 |
670,000 |
37,400 |
707,000 |
0.586 |
1.140 |
0.668 |
|
1990 |
722,000 |
38,700 |
761,000 |
0.631 |
1.121 |
0.707 |
|
1991 |
735,000 |
38,600 |
774,000 |
0.641 |
1.194 |
0.765 |
|
1992 |
566,000 |
39,400 |
605,000 |
0.501 |
1.164 |
0.583 |
|
1993 |
936,000 |
40,100 |
976,000 |
0.809 |
1.060 |
0.858 |
|
1994 |
728,000 |
39,200 |
767,000 |
0.636 |
1.085 |
0.690 |
|
1995 |
593,000 |
40,300 |
633,000 |
0.524 |
1.116 |
0.585 |
|
1996 |
652,000 |
39,600 |
692,000 |
0.573 |
1.044 |
0.598 |
|
1997 |
674,000 |
39,800 |
714,000 |
0.592 |
1.140 |
0.675 |
|
1998 |
707,000 |
39,700 |
747,000 |
0.619 |
1.107 |
0.685 |
|
1999 |
597,000 |
39,300 |
636,000 |
0.527 |
1.062 |
0.560 |
|
2000 |
430,000 |
38,900 |
469,000 |
0.389 |
1.116 |
0.434 |
(a) Depletions for 1995 are taken from the above table. These are scaled by year based on the ratio of total annual evaporation for the basin simulated by the VIC model for each year divided by that simulated for 1995 . Since the VIC simulation does not include 2000, the average depletion for the period was included here.
(b) Undepleted flow is the sum of gauge flow and depletions.
(c) Ratio uses values of runoff, including baseflow, from the VIC simulation for 1988-99. Average value is used for 2000.
The above methodology was applied on a monthly basis as well. This included scaling the annual depletions shown above for each year by the average monthly contribution of that month's evaporation to the annual total. In addition, a month-by-month development of the ratio of average VIC runoff above Vicksburg in mm/d to that for the entire Mississippi River basin was applied to the resulting monthly undepleted flows to extrapolate the Vicksburg runoff to the entire basin.